Molecule, layered medium and method for creating a pattern

ABSTRACT

The invention relates to molecules which can be attached to a substrate (4) and switched between different stable or metastable conformations (18, 19). At least one of these conformations (19) is generated and/or stabilized by the proximity of the substrate (4). The invention further relates to a layered medium comprising such molecules and to a method to switch such molecules in a controlled way. The layered medium is usable as resists for lithographic application, data storage media, and promoter of electron transfer between two media. The method is usable to generate and interrogate patterns in the layered medium.

TECHNICAL FIELD

The present invention relates to a molecule that is able to adhere tosurfaces of substrates in different conformations, a method ofpatterning layers of such molecules by switching them from oneconformation into another, and to the usage of such patterned layers forlithography, data storage, and display technology.

BACKGROUND OF THE INVENTION

The dramatic progress of computer technology over the past four decadeshas been fueled by an unparalleled development of the three basichardware elements: storage devices, processors and displays. In allthree areas, the art and science of surface structuring is of essentialimportance. The trends towards miniaturization and integration as wellas towards improved performance. reliability, and productivity requireincreasingly better control of surfaces and interfaces down to themolecular or atomic level.

Today. design rules for integrated circuits and storage devices havebecome so small that some of the most important conventional structuringtechniques got close to their principal limits. Standard opticallithography, for instance, is bound to dimensions larger than about onehalf wavelength which amounts to about 140 nm for uv radiation. Thebitsize of CD-ROMs is limited to about 0.5 micron because present-daylight-emitting diodes radiate red light with wavelengths of 800 to 1000nm. Obviously, new techniques are needed in order to further reduce thedesign rules.

With regard to display technology, the trend towards flat panel designsgenerates an increasing need for large, matrix addressable arrays ofpixel elements. Here, the technical problem is not miniaturization butenergy efficiency. yield and cost. At present, liquid crystal displays(LCD) play the major role in flat-panel technology. The LCD cell changesits optical transmissivity by appropriate application of voltage.Excellent contrast is achieved if arrays of thin film transistors (TFT)turn on and off the individual LCD cells. This scheme however. is costlyand TFT-LCDs are correspondingly expensive. Moreover, LCDs quitegenerally suffer from poor energy efficiency since they have to beilluminated by an external light source, the different colors resultingfrom filtering of white light. Because of these short-comings, thedisplay industry is greatly interested in potential alternatives to theLCD technology.

Light-emitting diodes (LED) are much more energy efficient than LCDs butthe presently available LEDs are too expensive for large-scale displaypanels. Present R&D activities in this field therefore concentrate inparticular on organic LEDs (OLED) which hold promise for low-cost massproduction. An overview about the design and properties of OLEDs can befound in the article by J. R. Sheats, H. Antoniadis, M. Hueschen, W.Leonard, J. Miller, R. Moon, D. Roitman, and A. Stocking "OrganicElectroluminescent Devices" which appeared in Science Vol. 273, p. 884,1996. In principle, OLEDs consist of layers of polymers sandwichedbetween a metallic and a transparent semiconducting electrode. The mainshort-coming of OLEDs is presently a short lifetime because of chemicalinteractions with the environment and degradation due to electroninjection at too high energies, necessitated by a poor match of theelectronic properties of the polymers with respect to the electrodematerials.

It is possible, however, to influence the electron injection capabilityby modification of the molecules next to the electrode/polymerinterface. A. Haran, D. H. Waldeck, R. Naaman, E. Moons and D. Cahendescribe in "The Dependence of Electron Transfer Efficiency on theConformational Order in Organic Monolayers", Science Vol. 263, pp.948-950, 1994, for instance, the influence of a monolayer ofoctadecyltrichlorosilane (OTS) molecules on the electron transfer (ET)process from a silicon electrode into an aqueous electrolyte solution.

The OTS layer can be switched by heating from one conformation intoanother. The different conformations correspond to different geometriesof a given molecule arising from bending or flexing of certain molecularbonds.

The authors found that current-voltage characteristics depend not onlyon the degree of coverage but also on the conformation of the OTSmolecules. In one example, the reverse current at a voltage of 0.2 Vchanged from 4.5 to 0.2 microamperes when the layer was transformed fromthe one into another conformation.

Research towards the controlled fabrication of small structures has beengreatly inspired by the success of scanning probe microscopes (SPM) inrecent years. Numerous examples confirm that the pointed probe tip ofthe SPM not only is able to monitor variations in the sample surfacestructure with atomic or near-atomic resolution but that it also can beused to modify the surface on a similar scale. It was demonstrated by T.A. Jung, R. R. Schlittler, J. K. Gimzewski, H. Tang, and C. Joachim inScience, Vol. 271, p. 181, 1996, for instance, that individual moleculescan be moved into prescribed fixed new positions and/or be modifiedwithout change of position under the influence of the SPM tip. In thepursuit of such investigations it was found that molecular flexibilityplays a crucial role for such manipulations.

Fixed ordered molecular layers on a substrate are generated, e. g. bymolecules forming Langmuir-Blodgett (LB) or self-assembled monolayer(SAMI) films or undergoing cooperative self assembly or being depositedby sublimation or by conformational epitaxy.

The molecules can exist in different conformations which arecharacterized by the (meta-) stable orientations and/or positions of thedifferent entities of which they are made up. The different entities ofthese molecules consist of individual atoms or molecule-likesub-entities of atoms which are more strongly bound among each otherthan to the atoms of the other entities. Frequently, the connectionsbetween individual entities arc single molecular bonds which can act asaxis for a relative rotational motion of the entities. Switching betweendifferent conformations usually comprises such rotational realignment ofentities. Molecules structured into such entities are standard inorganic chemistry.

OBJECT AND ADVANTAGES OF THE INVENTION

The invention combines fixation of switchable molecules to a substratewith the existence of several stable or metastable conformations toallow to determine and switch their conformation individually or withina certain region by external influence.

Appropriate combination of different entities allows to design moleculeswhich match the requirements of a certain application in oneconformation but are greatly different in another. Among the technicallyimportant properties which may undergo such variations are chemicalactivity, electrical conductivity, color, molecular dimensions, and thestrength of adhesion to the substrate. Conversely, these changes can beused to identify the conformation of a certain molecule or a layeredmedium of such molecules by a variety of interrogating techniques. Thedifferent conformations of such molecules are defined as the minima ofthe potential energy of the system molecule/substrate with respect toits configurational coordinates. It is usually possible to define arelevant configurational coordinate for each transition between twoconformations, such that the potential energy, when plotted as afunction of this coordinate, has at least two characteristic minima. Theposition and depth of these minima determine the structural arrangementof the entities in these conformations and their stability with respectto thermal excitation and/or external influences, respectively. Thedeepest minimum corresponds to the stable conformation of the molecule.All the other conformations are metastable. A molecule can exist in ametastable conformation for indefinite time if the energy barriersbetween the corresponding energy minimum and its neighbors is largeenough compared to the thermal energy which amounts to 25 meV at roomtemperature.

External influences which can provoke switching of conformation are, forinstance, a mechanical force which deforms the molecule to such anextent that it can snap into a different conformation like a macroscopicswitch, irradiation with light or elections that raises it into anexcited state state from which it can decay into the groundstate ofanother conformation, application of an electric field which lowers theheight and/or width of a particular energy barrier to such an extentthat the molecule flips into another conformation due to thermalexcitation or tunneling. In the following, the term "conformation" shalldesignate only those conformations of a molecule between which switchingby external influence is possible.

It is a first object of the invention to provide a class of moleculeswhich are attachable to a substrate in different conformations, at leastone of these conformations being generated and/or stabilized by theproximity to the substrate surface. Furthermore, these molecules areswitchable between at least two of these conformations by an externalinfluence, exerted by a structuring means.

Cu-tetra-(3, 5 ditertiary-butyl-phenyl) porphynrn (Cu-TBP-porphyrin)molecules, for example, freshly deposited onto a (100)-oriented Cucrystal surface in ultrahigh vacuum, remain in a conformation closelysimilar to that of the free molecules. In this conformation, theperipheral entities of the molecules are oriented normal to the plane ofthe central entity and the central entity is far enough away from thesubstrate surface to be only scarcely influenced by interaction forces.When pressed down by the tip of an STM, however, the central part getsso strongly attracted towards the substrate due to attractive, hereadhesive forces, that it remains in this second state even when the tipis removed: The system CuTBP-porphyrin/substrate is bistable, incontrast to the free molecule.

A molecule according to independent claim 1 for which Cu-TBP-porphyrinis an example consists of different entities and is attachable to asubstrate by means of physical adhesion and/or formation of chemicalbonds. This has the advantage that the position of these molecules isfixed at least in one dimension although the molecules may be free tomove along the surface of the substrate. It has the further advantagethat the substrate can balance a force exerted on the molecule duringswitching or that it can act as electrode if the molecule is to beexposed to an electric field. It is a further characteristic of themolecules according to claim 1 that one of the conformations is stableonly in the presence of the substrate. Specifically, one of the entitieschanges position with respect to the substrate during switching in suchway that the attraction between substrate and that entity is negligiblysmall in the first conformation but strong in the second conformationsuch that that entity closely and stably adheres to the substratesurface after switching. This has the advantage that molecules whichexist in one conformation only in free space can become bistable whenattached to a substrate and therefore can be used for the differentapplications described later. The drastic change of interaction with thesubstrate has the further advantage that the molecule can be completelyimmobile in the substrate-dominated conformation but movable along thesubstrate surface in the other conformation, or vice versa.

A molecule according to claim 2 has the advantage that it is fixed at acertain position on a substrate in at least one of its conformations andtherefore can be addressed individually by an interrogating orstructuring means. In particular, the structuring means can select amolecule and switch it from one conformation into another. The fixationof the molecule has the further advantage that the conformation of aparticular molecule or of a multitude of such molecules can bedetermined by an interrogating means locally and individually.

A molecule according to claim 3 has the advantage that it is switchableback and forth between two conformations repeatably which allows forapplications in display units or in write/read storage devices.

A molecule according to claim 4 has the advantage that it is builtaccording to a clear and hence well-realizable design concept: A centralentity can be designed to dominate the observable physical and chemicalproperties while one or several peripheral entities may then define theoverall structure of the molecule, potentially protect the centralentity, and/or form the `legs` which connect the molecule to thesubstrate. As a further advantageous feature of a molecule according toclaim 4, the distance of the central entity from the substrate can bechanged in the switching process, for instance by tilting the peripheralentities from an upright to a sideways position. As a consequence, themolecule may be moveable along the substrate surface in a firstconformation but completely fixed in a second. It further may be moreeasily removed by a solvent in the first conformation and have a largerheight than in the second. Also the characteristics of the electronicstates of a molecule can differ strongly in the two conformations.Optical properties such as the fluorescence of a molecule hence can varydrastically in the two conformations.

Many anticipated applications of the switchable, attachable moleculesaccording to claims 1 to 4 require the coverage, control and/ormodification over areas (much) larger than the size of individualmolecules. It therefore is a second objective of the invention toprovide a layered medium which comprises molecules according to claims 1to 4.

A layered medium according to claim 5 in the form of a completemonolayer has the advantage that it forms a dense film which effectivelyprotects the underlying substrate. Incomplete monolayers according toclaim 5, on the other hand, have the advantage to expose part of thesubstrate, hence provide access to this part by a modifying medium evenwithout removal of the layered medium.

A layered medium according to claim 6 has the advantage that themolecules are at a fixed position in any conformation. This is favorablein applications where the molecules are used as information carriers oras reversible switching elements, since they are then reproducablyaddressable.

A layered medium according to claim 7 has the advantage that themolecules of an incomplete monolayer continuously vary their lateralposition due to thermal excitation. Hence, part of the substrate is notpermanently covered by molecules, i. e. this part is exposed to theenvironment for certain periods of time and hence can be attacked by amodifying means during these periods. In the conformation where themolecules form a complete monolayer, on the other hand, the substratesurface is permanently shielded from the influences of the environment.

A layered medium according to claim 8 has the advantage that themolecules can act as local electric switches which regulate the electrontransfer from or to the substrate to or from a medium located above thelayered medium. The switching is made possible by an arrangement ofelectronic levels of the molecules in the layered medium whichfacilitates the emission of electrons from or to the substrate in oneconformation but is unfavorable for the emission in anotherconformation.

The application according to claim 9 is an important application of alayered medium, since by incorporation of the layered medium into anOLED, an electron injection layer is provided whose injection capabilitycan be turned on and off by a structuring means. The latter may provide,for instance, for a short voltage pulse applied to the two electrodes ofthe OLED. Alternatively, for example, piezoelectrically generatedpressure pulses may cause the switching. The function of the switchableelectron injection layer is similar to that of the thin-film transistorsused in present-day active LCDs.

Many anticipated applications of the layered medium according to claims5 to 9 require the generation of predetermined patterns in this layeredmedium and/or the underlying substrate. It therefore is a thirdobjective of the invention to provide a method that allows suchpatterning in a favorable way.

Claims 10 to 13 disclose different process variations that allow tostructure the layered medium and optionally the underlying substrate.

Claims 14 to 17 disclose methods that allow to generate patterns byexerting locally and in a controlled way one or several of the externalinfluences, such as a mechanical force which deforms the molecule tosuch an extent that it can snap into a different conformation like amacroscopic switch, irradiation with light or electrons that raises itinto an excited state state from which it can decay into the groundstateof another conformation or an application of an electric field whichlowers the height and/or width of a particular energy barrier to such anextent that the molecule flips into another conformation due to thermalexcitation or tunneling.

A method according to claim 10 has the advantage that it allows togenerate a predetermined pattern in a layered medium which consists ofareas where the molecules are in one conformation and other areas wherethey are in another conformation. The layered medium favorably isprepared in such a way that all the molecules originally are all in thesame conformation. The areas to be converted into the other conformationthen can be selected by an appropriate structuring means in a first stepand exposed to its influence in a second step.

A method according to claim 11 has the advantage that the moleculeswhich are in one of the conformations are selectively removed from thesubstrate leaving behind a predetermined pattern which consists of areaswhere the substrate is covered by the layered medium and other areaswhere the substrate surface is uncovered. A first molecule-removingmeans is used for this purpose which may be a solvent or a wet or dryetchant.

A method according to claim 12 has the advantage that the surface of asubstrate which was treated according to claim 10 and optionally claim11 can be structured in the shape of the pattern by exposing it to amodifying means which attacks the unprotected parts of the substratesurface. The modifying means can either remove material from or depositmaterial onto the unprotected areas of the substrate surface. Thisprocessing step is optional if a layered medium according to claim 7 isemployed since the latter allows access of a modifying medium to thesubstrate.

A method according to claim 13 has the advantage that the substrate isfreed from the residues of the layered medium, leaving behind thepredetermined pattern on the substrate surface. A secondmolecule-removing means may be used for this purpose which may be, likethe first, a solvent or a wet or dry etchant with the capability,however. to remove all the molecules which are or were part of thelayered medium. The complete removal has the advantage that it allows tofurther process the substrate as required, for instance, in theproduction of integrated circuit electronic elements.

Pattern generation by means of a movable, guided stylus according toclaim 14 has the advantage that extremely small parts of a layeredmedium on a substrate can be selected and switched. This allows to traceout correspondingly small size structures on the substrate. It is afurther advantage of this method that the shape of the pattern can bevaried freely by reprogramming of the path of the stylus along thesubstrate. The external influence of a stylus comprises, for example,mechanical pressure, exposure to an electric field or to a beam ofelectrons or photons. This method of pattern generation therefore isparticularly suited for applications where great flexibility isrequired, for instance for testing in research and development.

Pattern generation by means of a stamp according to claim 15 has theadvantage of great simplicity. In particular, it is possible to generatethe whole pattern simultaneously, even if it has a very complicatedstructure. Furthermore the pattern can be readily reproduced in largequantities. This method of pattern generation therefore is particularlysuited for mass production, for instance of compact disc-type read-onlystorage carriers using a layered medium according to claim 6 as storagemedium.

Pattern generation by means of an actuator array according to claim 16has the advantage that the pattern generator, i. e. the actuator array,can remain at a a fixed position with respect to the substrate. It is afurther advantage of this method that the shape of the pattern can bevaried freely by appropriate addressing of the array elements to beactivated. Parallel operation of a number of elements furthermore allowsfor high processing speed, in particular since mechanical motions arenot required. This method of pattern generation therefore isparticularly suited for applications which require frequent andreversible pattern change, for instance when used as switching elementsin write/read storage devices or in display devices.

The elements of the array can be, for example, electrodes, piezoelectricpestles or light sources such as illuminated apertures with shutters.Electrodes have the advantage that they expose the molecules of alayered medium locally to an electric field or an electron beam.Piezoeelectric pestles have the advantage that they can exert mechanicalpressure or send a shock wave into the layered medium. Light sourceshave the advantage that they can bring the molecules of the layeredmedium into an excited electronic state from which they may also decayinto a new conformation.

Pattern generation by means of an illumination or particle beamapparatus according to claim 17 has the advantage that commerciallithographic tools can be used for pattern generation.

It is also possible to combine several of the methods according toclaims 14 to 17 in a favorable way, for instance to use arrays of SPMtips for larger throughput in the patterning process.

Pattern interrogation according to claim 18 has the advantage that theconformation of the molecules in a certain area can be determined withthe same means that is used for pattern generation. This has the furtheradvantage that the generated patterns can be controlled for potentialerrors which possibly can be corrected on the spot. Another majoradvantage is the capability to determine the shape of an existingpattern which is required in the process of reading if the layeredmedium is used as a storage medium.

SUMMARY OF THE INVENTION

This invention deals with the application of a specific single molecule,a molecular assemblys, and a single molecular layer at an interfacetowards a substrate for data storage, as a new type of resist or in thecontext of various molecular devices. The principle of operation isswitching between conformations of the molecule which is created bydesign of functionality in the molecule together with the interfacingsubstrate. More particularly, it uses a molecular bi-stability which isbrought up through functional design of the molecule under considerationof the relevant properties of the interfacing substrate. Presentedembodiments include positive and negative resist applications,ultra-high-density storage.

The invention furthermore presents methods for the adressing andswitching of molecular properties, in particular electron transport andphoton emissivity.

The activation energies and mechanisms for switching the molecule fromone conformation into another may be chosen according to molecularstructure, internal flexibility and the integral interaction of themolecule with the substrate. The system molecule/substrate is optimallyadjusted when the potential barrier for switching is well above thermalenergies kT, wherein T denotes the temperature of reliable operation.

The molecule can be synthesized using existing methods. Theimmobilization of this molecule at the substrate surface enables the useof micro- and nano-fabrication tools and methods for optional furtherprocessing. The application of the molecule in a molecular layer as anew type of resist enables the generation of nanometer-scaled patterns.The disclosed molecule, layered medium, and method enable a broadapplicability and a variety of combinations with other established andexploratory methods.

Presented embodiments include resist applications, ultra high densitystorage, and display applications. The invention presents methods forthe addressing a location on a substrate, switching, and interrogationof molecular properties, in particular of the degree of adhesion to thesubstrate and electron transfer efficiency.

The large variety of molecules that fall into the class of the disclosedmolecule as well as the large variety of the disclosed methods enablesbroad range of applications and of combinations with other establishedand exploratory techniques.

DESCRIPTION OF THE DRAWINGS

Examples of the invention are depicted in the drawings and described indetail below by way of example. It is shown in

FIG. 1a: A molecule with a central entity and peripheral entities in afirst stable conformation.

FIG. 1b: A molecule with a central entity and peripheral entities in asecond stable conformation.

FIG. 1c: A substrate with three molecules in different stableconformations and with a stylus.

FIG. 2a: A molecule with four equivalent entities in a first stableconformation.

FIG. 2b: A molecule with four equivalent entities in a second stableconformation.

FIG. 3: The structure formula of Cu-tetra-(3,5ditertiary-butyl-phenyl)porphyrin (Cu-TB-porphyrin).

FIG. 4a: The potential energy of a molecule in free space (dashed curve)and near a substrate surface (solid curve) with respect to a particularconfigurational coordinate, whereby a potential well is generated by thevicinity to the substrate.

FIG. 4b: The potential energy of a molecule in free space (dashed curve)and near a substrate surface(solid curve) with respect to a particularconfigurational coordinate, whereby an existing potential well isenhanced by the vicinity to the substrate.

FIG. 5a: An arrangement for switching molecules of a layered medium inselected areas from one conformation into another one with a tip of anSPM.

FIG. 5b: An arrangement for switching molecules of a layered medium inselected areas from one conformation into another one with a stamp.

FIG. 5c: arrangement for switching molecules of a layered medium inselected areas from one conformation into another one with an electricactuator array.

FIG. 6a-e: Subsequent steps in a process of structuring the surface of asubstrate with an incomplete monolayer of switchable, attachablemolecules.

FIG. 7a-e: Subsequent steps in a process of structuring the surface of asubstrate with a complete monolayer of switchable, attachable molecules.

FIG. 8a: An arrangement for interogating the conformation of themolecules of a layered medium by means of a movable stylus which here isan STM tip.

FIG. 8b: diagram of the variation of the tunnel current when the tip inthe arrangement according to FIG. 8a moves along the surface of thelayered medium.

FIG. 9: An OLED with a layered medium with switchable, attachablemolecules, existing in two different configurations, one of them actingas electron injection promoter.

DETAILED DESCRIPTION OF THE INVENTION

In the following various exemplary embodiments of the invention aredescribed.

FIG. 1a schematically shows a molecule, consisting of a first entity 1which here is a central entity and two second entities 3 which here areperipheral entities. The first entity 1 is bound to the second entities3 via connections 2. The entities 3 adhere to a substrate 4 due to asecond attractive force 5. The molecule is in a first conformation 18where the central entity 1 and the peripheral entities 3 are oriented atright angles to each other. This orientation is energetically favorablewith regard to the directionality of the connections 2. The centralentity 1 is positioned at a distance from the substrate 4 where a firstattractive force 6 which here is a short-range adhesion force exerted bythe substrate 4 on the central entity 1 is small and hence not depictedhere. The interaction between the molecule and the substrate 4 due tothe second attractive force 5 is restricted to the parts of theperipheral entities 3 which are in the immediate proximity of thesubstrate surface. Therefore, the first conformation 18 is nearlyidentic to the stable conformation of the molecule in free space or insolution.

In FIG. 1b, the molecule is depicted in a second conformation 19 wherethe peripheral entities 3 are tilted sideways such that the centralentity 1 is closer to the surface of the substrate 4. The central entity1 now is under the influence of the strong attractive force 6 towardsthe substrate 4. The position of the central entity 1 is determined bythe balance of the additional attractive force 6 and a restoring forcegenerated by tilting of the connections 2. The second conformation 19does not exist when the molecule is in free space or in solution. Thetilt angle may be used as the relevant configurational coordinate ofthis molecule.

FIG.1c schematically shows the transformation, i. e. the switching of amolecule from the first conformation 18 into the second conformation 19under the influence of a stylus 7 which here is an SPM tip. The moleculeis part of a layered medium comprising a complete monolayer 15 of themolecules on the substrate 4. The SPM tip 7 forces a selected moleculeto switch by exerting, for instance, mechanical pressure on themolecule.

FIG. 2a, b show another type of molecule in the two conformations 18,19. The molecule consists of the first entity 1, the second entity 3 andtwo third entities 8, bound to each other in a closed chain by fourconnections 2. The four entities 1, 3, 8 are here compositionallyidentic. FIG. 2a shows this molecule in the first conformation 18 inwhich the entities 1, 3, 8 are arranged in the shape of a deformedsquare since the tilted shape of the connections 2 is energeticallyfavorable for the molecule. The second entity 3 adheres to the substrate4 via the second attractive force 5. The other entities 1, 8 are too faraway from the substrate 4 to experience a sizable attraction.

FIG. 2b shows the molecule in the second conformation 19 in which thefirst and second entities 1, 3 are lying flat on the substrate 4 and thethird entities 8 are lying on top of of the first and secondentities 1,3. The first entity 1 and the second entity 3 experience the attractiveforces 5 and 6, respectively, exerted by the substrate 4. The thirdentities 8 are attracted to the entities 1, 3 by a cohesive force 9. Theshape of the molecule in this second conformation 19 implies a strongdeformation of the connections 2. The resulting elastic forces arebalanced by the attractive force 6 and the cohesive force 9. One of thetilt angles of the connections 2 may be chosen as the relevantconfigurational coordinatefor this type of molecule.

FIG. 3 depicts the structure formula of Cu-tetra-(3,5ditertiary-butyl-phenyl) porphyrin (Cu-TBP-porphyrin), a molecule whichis able to exist on a substrate 4 in the two conformations 18 and 19according to FIG. 1. The central entity 1 is the Cu-porphyrin part. Theperipheral entities 3 are the four butyl-phenyl groups. The connections2 consist of the directional molecular bonds between C atoms of thecentral entity 1 and the peripheral entities 3, respectively. Theperipheral entities 3 are able to rotate around these C--C axes, theaverage tilt angle being the relevant configurational coordinate of thismolecule.

In the first conformation 18, as shown in FIG. 1a, the peripheralentities 3 are rotated out of the drawing plane by an angle of 90degrees around the C--C axis. The peripheral entities 3 thereforeprevent an approach of the central entity 1 to a substrate 4 beyond adistance given by the special extension of the peripheral entities 3with respect to their C--C axis. In the second conformation 19, as shownin FIG. 1b, the peripheral entities 3 are oriented almost parallel tothe drawing plane, thereby allowing close contact between the centralentity 1 and the substrate 4.

FIG. 4a, b schematically sketch the energy potentials E of the twomolecules shown in FIGS. 1 and 2, respectively, as a function of therespective relevant configurational coordinate φ. The dashed curves 10and solid curves 12 represent the potential of the molecules in freespace and next to the substrate 4, respectively. In FIG. 4a, the dashedcurve 10 has a potential minimum 11 and two potential maxima 14 whereasthe solid curve 12 has three potential minima, one higher potentialminimum I1 and two lower potential minima 13.

The single potential minimum 11 of the dashed curve 10 in FIG. 4aindicates that there is only one energetically favorable orientation infree space, namely that of the first conformation 18. When attached tothe substrate 4, two additional potential minima 13 result from thefirst attractive force 6 between the substrate 4 and the centralentity 1. The minima 13 are achieved at the values of the relevantconfigurational coordinate φ which are most unfavorable for a freemolecule, since they lie at the maxima 14 of the potential energy. Theminima 13 correspond to the second conformation 19. The existence of theseveral potential minima 13, 1 shows the capability to switch themolecule between two or more stable or metastable conformations.

For a molecule of the type shown in FIG. 2, the stable conformation infree space is that shown in FIG. 2a. The conformation of FIG. 2b is alsopossible in principle because of the cohesive force 9. The resultingpotential curve 10 is depicted as the dashed curve in FIG. 4b andtherefore has the nonequivalent minima 11, 13 already in free space butthe second minimum 13 is shallow. Thermal excitation therefore preventsthe molecule to remain in the corresponding conformation for extendedperiods of time. The substrate 4 stabilizes this second conformation dueto the first attractive force 6. This is expressed in the deep minimum13 of the solid curve 12 in FIG. 4b.

FIG. 5a to c show layered media with switchable molecules which here arearranged as complete monolayers 15 on the substrate 4 and threearrangements which allow to switch the molecules selectively inpredetermined areas such that patterns are created. The molecules areswitched from the first conformation 18 into the second conformation 19.The two conformations 18, 19 are indicated in the figures by lines of"H" and "/-/" symbols, respectively.

FIG. 5a shows pattern generation by use of a stylus 7 which may e. g. bean SPM tip. A horizontal movement of the stylus 7 at close distance tothe monolayer 15 switches the touched molecules from the firstconformation 18 into the second conformation 19. In order to leavepredetermined areas in the first conformation 18, the stylus 7 can beretracted while moving over these selected areas.

FIG. 5b shows pattern generation by use of a stamp 20 with protrudingparts 21. Predetermined areas of the monolayer 15 are to be switched.The protruding parts 21 exert a mechanical pressure on the areas of thelayered medium which forces the molecules of the areas of the monolayer15 to switch from the first conformation 18 into the second conformation19.

FIG. 5c shows pattern generation by use of an actuator array 30 withindividual actuators 31. Predetermined areas of the monolayer 15 areexposed to an electric field which switches the molecules of themonolayer 15 from the first conformation 18 into the second conformation19. The areas to be switched are selected by electric switches 32 whichconnect the individual actuators 31 with a voltage supply line 33. Thelatter is kept at a voltage U_(s) with respect to a second voltagesupply line 34 which is connected to the substrate 4.

FIG. 6a-e and FIG. 7a-e show the use of a monolayer of attachable,switchable molecules for patterning the surface of a substrate 4 in alithographic process. For this application, the monolayer 15 has thefunction of a resist.

FIG. 6a-e sketch the different steps necessary for a layered mediumwhich comprises a complete monolayer 15 consisting of the molecules inboth conformations 18, 19 which are firmly attached to the substrate 4,such as the molecules in the "H"-shaped conformation 18 of FIG. 1.

FIG. 6a and b show the monolayer 15 of molecules on top of the substrate4 before and after patterning by using, for instance, one of thearrangements sketched in FIG. 5 which convert the molecules from thefirst conformation 18 into the second conformation 19. In a next step,shown in FIG. 6c, the molecules in the first conformation 18 are removedwith a first molecule-removing means. Then, as shown in FIG. 6d, thesubstrate 4 together with the remaining molecules in the secondconformation 19 is exposed to a modifying means 42 which selectivelyattacks the uncovered areas of the substrate 4. Having reached a wantedlevel of modification which here is a prescribed etch depth as shown inFIG. 6d, the modification process is stopped by removing the layeredmedium form the modifying means 42 and the residues of the monolayer 15of molecules are removed with a second molecule-removing means, leavingbehind a topographic pattern on the substrate surface, as shown in FIG.6e.

FIG. 7a-e sketch an alternative lithographic process, applicable for amonolayer 15 which originally consists of the molecules in the firstconformation 18 in which they are mobile and form an incompletemonolayer 15 on the substrate 4. The second attractive force 5 betweenthe molecules in the first conformation 18 and the substrate 4 issufficiently small to allow thermal motion of the molecules along thesubstrate 4 such that a part of its surface is temporarily uncovered bythe molecules.

FIG. 7a, b show the monolayer 15 of molecules on top of the substrate 4before and after patterning by using, for instance, one of thearrangements sketched in FIG. 5 which convert the molecules from thefirst conformation 18 into the second conformation 19. In this secondconformation 19 the molecules are lying flat on the substrate 4, boundby the attractive forces (5, 6). They are covering the substrate 4completely over a predetermined area in this second conformation 19.

In a next step, shown in FIG. 7c, the substrate 4 with the molecularmonolayer 15 in the two conformations 18, 19 is exposed to the modifyingmeans 42 which selectively attacks the areas of the substrate 4 wherethe molecules in the first conformation 18 are floating on the substratesurface. Due to the thermally induced motion of the molecules themodifying means 42 reaches every place within the area where themolecules in the first conformation 18 are located. The molecules in thefirst conformation 18 may even happen to be removed from the substrate 4by the modifying means 42 since they are bound loosely only to thesubstrate 4. The molecules in the second conformation however shield thesubstrate 4 from being modified. The modification needs not be amaterial-removing step, but can also be a step of adding material, suchas growing a layer of any wanted material, using the molecules in thesecond conformation as a shielding mask.

The further steps of the process are the same as in the first processsketched in FIG. 6a-e, i. e. removing the modifying means 42 and hencestopping the etching process and also removing the molecules in thesecond conformation 19. The only difference between the two processes infact is the step of removal of those parts of the monolayer 15 whichremain in the first conformation 18, shown in FIG. 6b. This step is notnecessary in the second process since, in this case, the molecules inthe first conformation 18 are mobile on the surface of substrate 4 andhence do not permanently prevent the attack of the substrate 4 by themodifying means 42.

FIG. 8a illustrates the use of a layered medium with the attachable,switchable molecules in form of a monolayer with the two conformations18, 19 on the substate 4 as a storage medium. Information is stored inthe varying conformations 18, 19. Since the conformation 18, 19 may havean impact on size, electrical resistance, reflectivity, transmittivity,magnetic properties etc. , the alternation of one or several of theseproperties of the areas of the layered medium can be used to retrievethe stored information. The pattern may have been generated, i. e.written by using one of the arrangements sketched in FIG. 5. A stylus 7which here is the tip of a scanning tunneling microscope (STM) is movedalong the monolayer 15 in close, preferrably constant distance for thepurpose of interrogating, i. e. reading the information stored in thepattern.

FIG. 8b schematically shows a diagram of the tunnel current I_(t) versustime t. The tunnel current varies between two different values since thetunneling probability of electrons depends sensitively on theconformation 18, 19 of the molecules under the tip apex. The bit values"1" and "0" can be readily assigned to the two different values of thetunnel current I_(t).

FIG. 9 schematically sketches a cross section through an OLED whichincorporates, in contrast to the OLEDs known so far, a layered mediumwhich here comprises a monolayer 15 in two conformations 18 and 19. Theother elements of the OLED are, from top to bottom, a transparentelectrode 60, a continuous light-emitting polymer layer 61 and aconductive substrate 4. The substrate 4 and the transparent electrode 60are connected to a voltage U_(s) via voltage supply lines 33, 34.

The drawing also shows the electrons 62 injected from the substrate 4and photons 63 emitted from the polymer layer 61. The substrate 4 actsas electron-injecting counterelectrode to the transparent electrode 60.The electrons injected into the polymer layer 61 loose their energy bythe emission of the photons 63. The injection probability dependssensitively on the properties of the interface between the polymer layer61 and the substrate 4, i. e. the electron transfer (ET) capability ofthe monolayer 15. The electron transfer (ET) capability is determined bythe properties of the electronic states of the molecules. The latter aredifferent in the different conformations 18, 19 of the molecules.Appropriate design of the molecules in the monolayer 15 therefore allowsto switch such an OLED from a highly efficient light-emitting state intoa dark state and vice versa by changing from the first conformation 18,into the second conformation 19 of the respective molecules. Switchingbetween the conformations 18, 19 can be achieved in analogy to themethods with the arrangements described in FIG. 5, for instance byapplication of a short voltage pulse. Appropriate structuring of theelectrodes 4, 60 allows to turn on and off the electron transfer (ET)capability and hence the light emission in predetermined areas of theOLED. Such capability can be useful in display applications-of OLEDs,providing functions similar to that of the thin-film transistor switchesin active LCDs .

It can be summarized that the invention bases on a molecule beingseparateable into several entities 1, 3. The entities 1, 3 are more orless flexibly connected e.g. by binding electronic orbits 2. Theentities 1, 3 can be arranged stably or meta-stably at differentorientations with respect to each other, the different orientationscorresponding to different conformations 18, 19 of the molecules. Thestable orientations are given by the minima of the potential energy ofthe molecule with respect to the configurational coordinate orcoordinates characteristic for the different conformations 18, 19. Themolecules stably adhere to a desirable substrate 4 surface in at leastone of the different conformations 18, 19. The switching may comprise arelative, rotational and/or translational movement of the entities 1, 3with respect to each other and/or to the substrate 4.

In addition to the presented examples, the switching of molecularconformation in the context of data storage, lithography, molecularelectron transport and light emission from optoelectronic devices it isimportant to point out that conformation in general determines anyphysical and chemical property of molecular systems. Thus, the presentedmethods for design, integration and adressing of the molecularconformation can be combined with most other physical and chemicaldetection mechanisms. The mentioned tools and methods can be combinedwith each other and with other techniques for detection, or assembly offunctional nanoscale structures. In particular, said techniques can becombined with any sensing method as cantilever-based sensors, vibratingreed magnetometer, NMR, ESR, immunosensors, wave guide and diffractionoptical sensors, single photon detection/single molecule spectroscopysetups. Also alternative properties can be controlled/switched using thedisclosed schemes. In general, any chemical functionality, e. g.chromophority, photochromic activity, electrochromic activity, catalyticactivity, enzymatic activity, drug activity, specific reactivity, spinlabels, immuno activity, NMR labels, hormones, potentially combines withconformational switching/activation. Examples are the patterning orcontrol of superconductivity in organic superconductors, the control ofselective chemical reactivity, for example given by a radical that ishidden in one of the conformations and exposed to some reactant in theother conformation, or the variation of magnetic, and electronicproperties of layers, e. g. layer magnetism, optical reflectivity, thatgo beyond the above mentioned examples. Mixtures of designedconformational systems can be utilized to expose specific properties.Using the above mentioned example of specific reactivity hidden in aconformational inactive form, different reaction precursors may bespecifically integrated. Beyond the integration techniques specificallymentioned in the examples, particle beam and optical lithography as wellas stamping, other techniques for excitation of conformational forms andthe assembly and integration may well prove use, such as contact forces.As well chemical self-assembly techniques, LIGA, all advanced andexploratory means to lithographically integrate functional structures,as well as the advanced `bottom up` integration techniques may be used.

Any write medium can also be used as read medium. Generally, any readmechanism can be used.

We claim:
 1. Molecule comprising at least two entities (1, 3) which arebound to each other by at least one connection (2) and being attachableto a substrate (4) and being switchable under an external influencebetween at least two different stable or metastable conformations (18,19) which are distinguishable by a different arrangement of saidentities (1, 3) with respect to said substrate (4) and/or to each other,characterized in that, when said molecule is attached to said substrate(4), in a first of said conformations (18) said molecule is attracted tosaid substrate (4) by means of a second attractive force (5) between asecond (3) of said entities (1, 3) and said substrate (4) and a first(1) of said entities (1, 3) has a position with respect to saidsubstrate (4) at which a first attractive force (6) between them isnegligible versus said second attractive force (5) and that in a secondof said conformations (19) said first entity (1) has a position at whichit is bound to said substrate (4) by said first attractive force (6). 2.Molecule, according to claim 1, characterized in that the position ofthe molecule on the substrate (4) is fixed in at least one of theconformations (18, 19).
 3. Molecule, according to claim 1 or 2,characterized in that the molecule is switchable reversibly between thefirst and the second conformation (18, 19).
 4. Molecule, according toone of claims 1-3, characterized in that the first entity (1) has acentral position within the molecule and that the second entity (3)comprises at least one peripheral entity which is movably connected tosaid first entity (1).
 5. Layered medium, comprising a plurality ofmolecules according to one of claims 1 to 4, arranged in the shape of acomplete or incomplete monolayer (15) on a substrate (4).
 6. Layeredmedium according to claim 5, characterized in that the molecules remainat fixed positions on the substrate (4) in all conformations (18, 19) aswell as during switching.
 7. Layered medium according to claim 5,characterized in that the molecules in at least one of the conformations(18, 19) are movable along the substrate (4) and that said molecules arein continuous motion along the substrate (4) due to thermal excitationsuch that an area of said substrate (4) is temporarily uncovered, andthat in at least one other of said conformations (18, 19), saidmolecules remain in a fixed position on said substrate.
 8. Layeredmedium according to one of claims 5 to 7, characterized in that thesubstrate (4) is electrically conductive, and that in one of theconformations (18, 19), the molecules favor a capability of saidsubstrate (4) to emit electrons into an adjacent non-metallic medium andthat in another of said conformations (18, 19) said electron emissioncapability is smaller.
 9. Layered medium, according to claim 8,characterized in that it is at least a part of an electron injectionelectrode of an organic light-emitting diode whose light emissioncapability is switchable between various efficiencies by switchingbetween the conformations (18, 19) of the molecules of said layeredmedium.
 10. Method for creating a predetermined pattern in a layeredmedium according to one of claims 5 to 9, characterized in that in afirst step a region of said layered medium is selected and in a secondstep said selected region is exposed to a structuring means whichswitches said molecules in said selected region from one of theconformations (18, 19) into another of said conformations (18, 19). 11.Method for creating a predetermined pattern according to claim 10,characterized in that in a third step the molecules in one of theconformations (18, 19) are removed with a first molecule-removing means.12. Method for creating a predetermined pattern according to claim 10 or11 characterized in that in a following step, the substrate (4) ispatterned using the molecules, which after the previous step haveremained in a fixed position on said substrate (4), as a patterningmask.
 13. Method for creating a predetermined pattern according to oneof claims 10 to 12, characterized in that in a last step the moleculesare removed from the substrate (4) by a second molecule-removing means.14. Method for creating a predetermined pattern according to one ofclaims 10 to 13, characterized in that as the structuring means at leasta stylus (7) is used, which performs the switching function and ismovable along the layered medium on a path that corresponds to the shapeof the pattern to be created.
 15. Method for creating a predeterminedpattern according to one of claims 10 to 13 characterized in that as thestructuring means at least a stamp (20) is used, which performs theswitching function and which comprises protrusions (21), structuredaccording to the pattern to be created.
 16. Method for creating apredetermined pattern according to one of claims 10 to 13, characterizedin that as the structuring means at least an actuator array (30) isused, which performs the switching function and is, for creating thepattern, arranged in proximity of or in contact with the layered mediumand whose actuators (31) are individually activatable.
 17. Method forcreating a predetermined pattern according to one of claims 10 to 13,characterized in that as the structuring means at least an illuminationapparatus or particle beam apparatus is used.
 18. Method forinterrogating a pattern in a layered medium according to one of claims 5to 9, or on a substrate, characterized in that the structuring meansaccording to one of claims 14 to 17 is used as interrogating means.